Alright, so I just finished up with my first E-85 rotary tune yesterday.

https://i.imgur.com/mM1vcNY.jpg

I'm super happy with the results.

Upper line is after the dyno.

The lower line is before dyno tuning, but after a bunch of street tuning.

'07 RX8. ~85k miles. Original engine. Original coil packs.

E85. Stock injectors. Walboro GSS242 fuel pump. Stock intake. OEM air filter. SOHN OMP adapter. Redline 40504 alcohol specific 2 stroke oil. Turbo XS header. AP catless midpipe. Borla catback. Rear O2 sensor delete.

For reference, this car made 179whp on the same dyno before all of the mods. Dyno Dynamics units typically read a teensy bit low. The engine was healthy as **** at 80k miles when I first got the car. I'm the second owner. First owner was a psychotic about maintenance.


The full load stuff is dead bang on. I'd add fuel, it would lose a bit of power. Go leaner it would lose a bit of power or stay the same. Same story with adding/subtracting timing.

I had a bit of time to do partial load stuff on the dyno. Not a lot of time though.

I know the part throttle stuff could still be better. I'm sure there is a lot of stuff still in the mapping that could still be better.

Attached is my AP map. Feel free to pick it apart and tell me what I can improve. I was seeing some weird closed -> open loop transition stuff on the dyno. I'm going to have to experiment more with that.

 

How can you make more power with a fuel with a lower energy content?

 

By burning ~22% more of it.

It's also 105 octane. About 3.5 degrees of timing advance everywhere vs. stock on the leading plug. Almost double that much more advance on the trailing side.

E-85 also has a slower flame front propagation speed. This is very beneficial to the very long combustion cycle against the rotor face.

 

You should definitely try to properly tune an e5\e10 car.
Ethanol's advantage aren't as great as they seem.

 

Congrats! By the way, I have not read everything but I must say: Please change those coils. No RX-8 has good coils at 85k miles.

Good luck.

Paul.

 

I checked them with my o-scope when I first got the car. They still look healthy. Great primary discharge voltage and good spark duration. Firing through alcohol with stock plug gaps would definately expose weakness.

 

If you do actual math, you will find that fixed amount of air mixed with E85 releases about 6% more heat than same amount of air mixed with gasoline, at given lambda.

Then you have higher engine efficiency, as combustion occurs at lower temperature - lower losses into coolant and oil.

Alcohol fuels have longer initial flame kerner development, but once the flame front is established, burn rate is faster then with gasoline, use of strong ignition system can actualy allow for lower timing advance to reach best torque then with gasoline, which means less negative work in engine, more net output.

Higher knock resistance allows operation without timing retard from MBT and we all know that rotary engine is severely limited platform in this regard, so again, power increase from optimal operation.

And last, but not least, significant evaporative cooling increases volumetric efficiency and again, permits optimal operation in knock limited situation.

Alcohol fuels have only one disadvantage, higher required fuel mass to reach same lambda. Thing is, that engine fully optimized for ethanol fuel would operate at higher compression and boost pressures and without timing retard and fuel enrichment so actual fuel consumption wouldn't be that much higher than with gasoline. E85 requires 50% more fuel mass to reach same lambda, but boosted rotary on gasoline requires as much as 40% enrichment, resuting consumption in such situation would be just 10% higher...

 

has anyone test with e85 oem map ? Is it works or gains anything ? Great numbers

 

E-85 in a car with stock ECU mapping would really struggle to stay running. You need to make large fueling changes for things to work.

 

Thanks for taking the time to write that.

To add a bit of real world anecdote about thermal transfer and evaporative cooling.

My coolant temps average about 10-15 degrees F cooler than on gas.

Another thing you didn't mention is the complete lack of any carbon deposition from E-85. Carbon has always been a huge problem with rotaries. I'm excited for this engine to need a teardown, just so I get to see how clean and shiny everything will be.

 

Thanks for the explanation. So in his case he is using around 50% more fuel in your opinion?

 

Are you using cobb ? Which parametres are you change for e85 ?

 

In case of pure ethanol vs. pure gasoline, comparison of lower heating values reveals that ethanol would need as much as 64% more fuel mass than gasoline to release same amount of heat. But due to higher fuel density of ethanol, it would show up as about 50% higher volume.

In case of usual E10 gasoline vs. E85, later would need 40% more fuel mass which is about 33% more volume.

So we can see that disadvantage of lower fuel economy can be quite significant in conditions which aren't knock limited - low load driving, NA engines, but considering that high boost rotary engines are tuned for about 0.73 Lambda on gasoline, and E85 fueled ones comfortly for 0.85 Lambda, actual difference in used fuel volume would be just 10% higher for E85.

 

Injector scaling is the big one.

Everything else is pretty standard.

 

FWIW, I ended up having to add about 22% more fuel everywhere when all was said and done. Some places a few % more, some places a few % less.

I tuned to .85 lambda.

I haven't been able to really get an accurate gauge of mileage of gas vs. E-85. Too much time spent driving like a gleeful idiot.

My best tank of E-85 in 100% city driving so far has been ~13mpg. My best tank of gas in the exact same driving environment was around ~16mpg.

With the fuel prices locally, it's actually SLIGHTLY cheaper to run E-85 right now despite the crap mileage. You're talking pennies per gallon though, so it's not a huge deal. When winter rolls around and the price gaps mostly goes away, I will switch back to gas. I'll get back on the dyno then to get a valid comparison.

 

One of the biggest problems for having a car tuned for e85 is traveling. e85 isn't available at every gas station. You could get yourself into a situation where you need fuel and it isn't available. This would be an even bigger problem once your outside of the corn belt.

 

The AP has multiple maps.

I have a map for gas, I have a map for E-85, I also have a map for a 50/50 mix. The O2 sensor can do some pretty huge fuel trims for anything between the 3 maps.

The gas maps just haven't been dyno tuned. I used my dyno tuned E-85 map as a starting point, then made changes as appropriate. It's not perfect, but it's probably closer than your average car running a bunch of bolt ons with no tune.

 

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x2.

 

nvermind subbed

do you premix as well as inject the redline?

 

No premix. From all of the reading I have done, I don't see a need for it.

I have increased the OMP oil delivery across the entire operating range. There should be plenty of rotor lubrication. The redline stuff is very clingy.

 

Lol, i know very little about fuels, that's why I asked.

 

wouldnt doing this resolve alot of the engne flooding issues from shutting it of when cold? considering it burns fuel at a much faster rate....

 

E85 would be a dream to use given the same reliability and ease of use. Especially considering the fact that 1 litre of 95 is $2.60 here, and 1 litre of E85 is $1.63.

 

Indy cars secretly rely on nuclear flux capacitors to go 220 mph, not ethanol fuel

You'd be surprised to know how much E% you can use in an Rx8 with just by tuning the factory components

The biggest issue for street or track is we only have a 13.5 gallon fuel tank, which essentially becomes an 8 gallon tank with the E85 consumption rate